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I know of the conceptualized "Sinkers", "Floaters" and "Hunters" that Carl Sagan and Edwin Salpeter of Cornell conceived of - as possible life forms that might inhabit a gas giant. At the time they conceived of this, there was no real info about the amount of amino acids that might exist in the atmospheres of planets like Saturn and Jupiter. We have also learned a lot more about the composition of these planets. I am wondering if these life form ideas are still possible alien life forms that could develop in a gas giant of some type.

Based on the temperatures and composition of Sudarsky class II planets - which are closer in to the star. Supposedly temperatures become too warm for ammonia ice to be stable. Instead, Class II gas giants have clouds of water vapor, giving them a high albedo and a beautiful blue-white coloration.

Would the possibility of life of some kind be able to develop there and thrive? Would it mostly be microbial if anything? Would larger multicellular beings be possible in the forms Sagan and Salpeter dreamed of or some other form? Would it have to be Anaerobic? Could it have developed on a more terrestrial form of the planet before it grew to a gas giant?

I am curious about the possibilities of this for a story, but I want to make it at least believable even if it is just an unlikely chance of a life form of a kind we might not even recognize as life as we define it.

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    $\begingroup$ Hi! There's a lot of question marks and any time that's happened I've seen the question get put on hold. Maybe reduce the questions to just one. Also make sure not to make it cover too much otherwise it might get put on hold for that. :D $\endgroup$ – SlothsAndMe Jan 24 at 4:38
  • $\begingroup$ good to have you join the world building community. $\endgroup$ – Haha TTpro Jan 24 at 4:48
  • $\begingroup$ Thank you! Happy to have found it! $\endgroup$ – GRF Jan 24 at 6:52
  • $\begingroup$ @GRF I am interesting and I would like to read your work (or your previous work if any) $\endgroup$ – Haha TTpro Jan 25 at 18:23
  • $\begingroup$ Thanks @HahaTTpro - I don't have any stories published at the moment but I am working a few ideas, one that will be in an anthology that a few writers are collaborating on, and I might do a few things in personally published books sometime if I can. $\endgroup$ – GRF Jan 26 at 0:56
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In terms of life developing on a gas giant? Sure, it's possible. At best you could have some form of single cell extremophile organism in the uppermost atmosphere. Even this however is unlikely, as Gas Giants are stupidly hot; what their outer atmospheres lack in heat they make up for in cell crushing pressure.

Gas Giants

Heat, pressure and agitation (cause by the rapidly moving atmosphere) all increase entropy, which is bad for life. In fact Schrodinger coined the term negentropy, meaning negative entropy or tendency towards order, to describe the fundemental characteristic of life. Thus, an environment with super high entropy seems unlikely to produce life of any form, let alone complex multi-cellular organisms.

Gaseous Terrastrial Planets

Instead you should look towards something like venus. Venus is not a gas giant, but it does have a super dense atmosphere. For this reason it is pretty much impossible for multi-cellular organisms to form, however those extremophile organisms do have a chance of existing in its outer atmosphere.

To increase the chances of these organisms existing, Venus used to be an earth like planet, perhaps even with large water deposits on it's surface. These oceans (if they existed) would have been ideal breeding grounds for life. Unfortunately the runaway greenhouse effect made all the oceans evaporate and thus destroy these breeding grounds.

If you want to continue with this concept, you could say that during this pre-evaporation period complex intelligent life evolved. Predicting their planets eventual demise, they could move to floating cities. While living on these floating platforms, they could evolve further to survive independantly of the platforms; perhaps developing wings to travel between cities and lungs capable of breathing in the new atmosphere.

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  • $\begingroup$ Would it make a difference if the gas giant was a different type? I was trying to find examples of cloud layers, temps and pressure for Sudarsky class II giants which seem to have more water vapor in one of the medium layers and they have more moderate temperatures there. Pressure is still high but seems like a life form could adapt to that. Would life be more likely in a Type II vs I or other variety of Gas Giant? $\endgroup$ – GRF Jan 24 at 17:05
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    $\begingroup$ As I said in the answer it is technically possible, I just wouldn't bet on it. See Sudarsky class II giants are actually more like big old water clouds, but that's not to say the water is constructive to life. class II giants tend to be around -23 degrees celcius, which means that any water will exist as ice crystals or as water vapour, neither of which is conducive to development of life. This is because $\endgroup$ – corvus_poe Jan 25 at 6:10
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    $\begingroup$ of the fact that water is only really useful to life because of its chemical properties (see polarity and thus solubility) that are present when it is in liquid form. the Angular bonds between molecules are overcome when in gas form, and are too strong to be useful to life when in solid form $\endgroup$ – corvus_poe Jan 25 at 6:18
  • $\begingroup$ Your Venus creature also has to be able to withstand non stop huge 350kph wind and acid rain. Venus is a terrible place. $\endgroup$ – Trevor D Jan 29 at 18:05
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My idea:

  • Living in gas (dense gas): let's image the environment is a large sea of gas. Species could be a fish-like species that swimming in gas planet, or balloon like species (jelly-fish, maybe) at consume gas and floating around, becoming food for others gas predator.

  • Living in gas (not so dense gas): let's image the environment is a large sky with no bottom. Species could be bird-like or balloon-like

  • Living on island: there are floating piece of land in gas planet where creature can live on. Those creature can look like Earth, land-based creature (including tree)

A planet could have multi layer

  • outer: not-so-dense gas, large sky, not many animal live here because not enough gas, difficult to breath.

  • middle: not-so-dense gas, with a lot of island. People could live on those island.

  • inner: dense to very dense (perhaps toxic as it go deeper) gas.

Some point of reference:

In Star Wars, there are creature called Purrgil, perhaps you can use as point of reference.

"Purrgil were a species of massive, whale-like creatures that lived in Deep space, traveling from star system to star system. It was their natural ability to fly through hyperspace that inspired sentients to develop the hyperdrive technology"

"n order to breathe, these space-whales needed to inhale stores of a specific green gas, Clouzon-36."

Purrgil is a whale that flying in space, and it feed on gas (Clouzon-36 - a kind of fuel for hyperspace) on specific gas planet. They do have ability to dive into the gas planet to inhale the gas.

See cartoon Star Wars Rebels - The Call for Purrgil behaviour.

The game AIRHEART - Tales of broken Wings build the world of floating island. It is good idea to check it out for the concept of "floating island" in not so dense gas planet.

I suggest reading Can airborne floating/flying islands be scientifically possible? for more reference on floating islands.

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  • $\begingroup$ "no bottom. Species could be bird-like" - where would they nest? $\endgroup$ – Alexander Jan 24 at 17:46
  • $\begingroup$ @Alexander they can nest on islands (piece of floating large ground that stable) $\endgroup$ – Haha TTpro Jan 25 at 18:12
  • $\begingroup$ so the idea #2.1 is not sustainable without idea #3? $\endgroup$ – Alexander Jan 25 at 19:51
  • $\begingroup$ @Alexander is it require a land for bird to nest, or do the bird need to nest at all ? Ex: bird can make floating nest on stable air current, using floating material like body of dead species (dead, body part) or big living species (bird like flea with your dog). Or bird don't need to nest at all. Species adapt. $\endgroup$ – Haha TTpro Jan 28 at 11:15
  • $\begingroup$ "stable air current" - that's the idea that you can actually add to your answer. $\endgroup$ – Alexander Jan 28 at 17:34
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As an additional reference you might want to have a look at the origins of the hive in Destiny, which were living on floating islands somewhere within a gas giant. It might also be interesting to see how they described the world and how this story developed, so I recommend looking at the books of sorrow which flesh the story out a bit.

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